1. Field of the Invention
The present invention relates to a method for forming a magnetic pole layer of a thin film magnetic head having at least an induction type magnetic transducer, a thin film magnetic head and a method for manufacturing the same.
2. Description of the Related Art
Recent improvement of the surface recording density of hard disk drives has resulted in demands for improved performance of thin film magnetic heads. Commonly used thin film magnetic heads are composite thin film magnetic heads having a structure in which a recording head having an induction type magnetic transducer for writing and a reproduction head having a magnetoresistive (hereinafter referred to as xe2x80x9cMRxe2x80x9d) element for reading are stacked into layers. MR elements include AMR elements utilizing the anisotropic magnetoresistive (hereinafter referred to as xe2x80x9cAMRxe2x80x9d) effect and GMR elements utilizing the giant magnetoresistive (hereinafter referred to as xe2x80x9cGMRxe2x80x9d) effect. A reproduction head utilizing an AMR element is referred to as xe2x80x9cAMR headxe2x80x9d or simply as xe2x80x9cMR headxe2x80x9d, and a reproduction head utilizing a GMR element is referred to as xe2x80x9cGMR headxe2x80x9d. An AMR head is used as a reproduction head having a surface recording density in the excess of 1 gigabit/inch2, and a GMR head is used as a reproduction head having a surface recording density in the excess of 3 gigabit/inch2.
An AMR head has an AMR film having the AMR effect. A GMR head has the same structure as that of an AMR head except that the AMR film is replaced with a GMR film having the GMR effect. When exposed to the same external magnetic field, the resistance of a GMR film changes more significantly than that of an AMR film. Therefore, it is said that the reproduction output of a GMR head can be about 3 to 5 times greater than that of an AMR head.
One method for improving the performance of a reproduction head is to change the MR film. In general, an AMR film is a film which is made of a magnetic material having the MR effect and which has a single-layer structure. On the contrary, most GMR films have a multi-layer structure which is a combination of a plurality of films. The GMR effect produces several types of mechanisms, and the layer structures of GMR films depend on the mechanisms. GMR films proposed in the past include superlattice GMR films, granular films and spin valve films, and spin valve films are promising as GMR films which must have a relatively simple configuration, which must exhibit significant fluctuation of resistance even in a weak magnetic field and which are to be mass-produced. Therefore, the purpose of improving the performance of a reproduction head can be easily achieved by, for example, changing the material of the MR film from an AMR film to a GMR film or the like having excellent sensitivity to magnetoresistance.
Factors that determine the performance of a reproduction head other than the choice of the material as described above include the pattern widths, especially MR height. MR height is the length (height) of an MR element from the end thereof where the air bearing surface (surface facing the medium) is located to the opposite end thereof. The MR height is essentially controlled by the amount of lapping during the processing of the air bearing surface.
The trend toward reproduction heads having improved performance has resulted in a need for improvement of recording heads. In order to improve the performance of a recording head especially the recording density, the track density of the magnetic recording medium must be increased. For this purpose, it has been desired to provide a recording head having a narrow track structure by processing a magnetic layer for forming an top magnetic pole on a submicron basis utilizing semiconductor processing techniques.
Another factor that determines the performance of a recording head is the throat height. Throat height is the length (height) of a region that extends from the air bearing surface to an edge of an insulation layer for electrically isolating a thin film coil (the region is referred to as xe2x80x9cmagnetic pole portionxe2x80x9d in this application). There is a need for a reduction of the throat height to improve the performance of a recording head. The throat height is also controlled by the amount of lapping during the processing of the air bearing surface.
As described above, in order to improve the performance of a thin film magnetic head, it is important to form the recording and reproduction heads with preferable balance between them.
A description will now be made with reference to FIGS. 26 through 36 on an example of a method for manufacturing a composite thin film magnetic head according to the related art. FIGS. 26 through 36 show a section perpendicular to an air bearing surface.
According to the manufacturing method, as shown in FIG. 26, an insulation layer 102 made of, for example, alumina (Al2O3) is deposited on a substrate 101 made of, for example, aluminum oxide and titanium carbide (Al2O3.TiC) to a thickness in the range from about 5 to 10 xcexcm. Next, as shown in FIG. 27, a bottom shield layer 103 for a reproduction head is formed on the insulation layer 102.
As shown in FIG. 28, for example, alumina is then deposited on the bottom shield layer 103 to a thickness in the range from 100 to 200 nm by means of sputtering to form a shield gap film 104. Then, an MR film 105 for forming an MR element for reproduction is formed on the shield gap film 104 to a thickness of several tens nm and is patterned into a desired configuration using photolithography with high accuracy. As shown in FIG. 29, a shield gap film 106 is then formed on the shield gap film 104 and MR film 105 to embed the MR film 105 between the shield gap films 104 and 106.
Next, as shown in FIG. 30, a tom shield layer-cum-bottom magnetic pole layer (hereinafter referred to as xe2x80x9cbottom magnetic pole layerxe2x80x9d) 107 made of a magnetic material, e.g., permalloy (NiFe) to be used for both of reproduction and recording heads is formed on the shield gap film 106.
As shown in FIG. 31, a recording gap layer 108 constituted by an insulation film, e.g., an alumina film, is then formed on the bottom magnetic pole layer 107, and a photoresist layer 109 is formed on the recording gap layer 108 in a predetermined pattern using photolithography with high accuracy. Next, a first layer thin film coil 110 for an induction type recording head made of, for example, copper (Cu) is formed on the photoresist layer 109 using a plating process.
Next, as shown in FIG. 32, a photoresist layer 111 is formed on the photoresist layer 109 and coil 110 in a predetermined pattern using photolithography with high accuracy. Then, a heating process is performed at a temperature of, for example, 250xc2x0 C. to planarize the photoresist layer 111 and to provide insulation at the gaps of the coil 110.
Next, as shown in FIG. 33, a second layer thin film coil 112 made of, for example, copper is formed on the photoresist layer 111 using, for example, a plating process. Then, a photoresist layer 113 is formed on the photoresist layer 111 and coil 112 in a predetermined pattern using photolithography with high accuracy, and a heating process is performed at a temperature of, for example, 250xc2x0 C. to planarize the photoresist layer 113 and to provide insulation at the gaps of the coil 112.
Next, as shown in FIG. 34, the recording gap layer 108 is partially etched for forming a magnetic path in a position behind (right-hand side in FIG. 34) the coils 110 and 112. Then, a top magnetic pole layer 114 made of a magnetic material, e.g., permalloy, for the recording head is formed on the recording gap layer 108 and photoresist layers 109, 111 and 113. The top magnetic pole layer 114 is in contact with the bottom magnetic pole layer 107 in a position behind the coils 110 and 112 to be magnetically coupled therewith. Next, the recording gap layer 108 and bottom magnetic pole layer 107 are etched by about 0.5 xcexcm by means of ion milling using the top magnetic pole layer 114 as a mask, and an overcoat layer 115 made of, for example, alumina is formed on the top magnetic pole layer 114. Finally, mechanical processing of a slider is performed to form an air bearing surface 120 of the recording and reproduction heads, which completes a thin film magnetic head.
FIGS. 35 and 36 show the completed thin film magnetic head. FIG. 35 shows a section of the thin film magnetic head perpendicular to the air bearing surface 120, and FIG. 36 shows an enlarged view of a section of the magnetic pole portion parallel with the air bearing surface 120. In FIG. 35, TH represents the throat height, and MR-H represents the MR height. In FIG. 36, P2W represents the width of the magnetic pole, and P2L represents the thickness of the magnetic pole portion.
Factors that determine the performance of a thin film magnetic head other than the throat height, MR height and the like include an apex angle as indicated by xcex8 in FIG. 35. The apex angle is an angle defined by a straight line connecting the corners of the photoresist layers 109, 111 and 113 at the side thereof closer to the air bearing surface and the upper surface of the top magnetic pole layer 114.
The structure as shown in FIG. 36 in which the side walls of the top magnetic pole layer 114, recording gap layer 108 and a part of the bottom magnetic pole layer 107 are formed in self-alignment with each other in the vertical direction is referred to as xe2x80x9ctrim structurexe2x80x9d. The trim structure makes it possible to prevent any increase in the effective track width attributable to the expansion of magnetic flux that occurs during writing of the narrow track. As shown in FIG. 36, lead layers 121 are provided on both sides of the MR film 105.
A composite thin film magnetic head manufactured as described above has many problems associated with especially the positional relationship between the recording head and reproduction head, and such problems have often resulted in deterioration of the characteristics and reliability of the composite thin film magnetic head as a whole and have reduced the yield significantly.
In order to improve the performance of a thin film magnetic head, it is important to accurately define the throat height TH, MR height MR-H, apex angle xcex8, magnetic pole width P2W and magnetic pole length P2L.
The present application addresses especially a problem associated with the accurate control of the magnetic pole width P2W (hereinafter referred to as xe2x80x9cfirst problemxe2x80x9d) and a problem associated with the accurate control of the throat height TH (hereinafter referred to as xe2x80x9csecond problemxe2x80x9d).
The first problem will now be described. The magnetic pole width P2W must be defined accurately to determine the track width of a recording head. Especially, dimensions on the order of 1.0 xcexcm or less are required in these days to allow recording at a high surface recording density, i.e., to form recording heads having a narrow track structure. For this purpose, the top magnetic pole layer that determines the magnetic pole width P2W must be finely formed.
The top magnetic pole layer is formed using, for example, a frame plating process as disclosed in Japanese Patent Laid-Open Publication No. 7-262519. When the top magnetic pole layer 114 is formed using the frame plating process, sputtering is performed to form a thin electrode film made of, for example, permalloy on a coil portion (hereinafter referred to as xe2x80x9capex portionxe2x80x9d) which is covered by the photoresist layers 109, 111 and 113 to be built up in the form of a mound. Next, photoresist is applied thereon and is patterned using photolithography to form a frame (outer frame) for plating. The top magnetic pole layer is then formed using a plating process using the previously formed electrode layer as a seed layer.
The apex portion has a height difference of, for example, 7 to 10 xcexcm or more. The photoresist is applied on the apex portion to a thickness in the range from 3 to 4 xcexcm. When the photoresist on the apex portion must have a thickness of at least 3 xcexcm, since the photoresist which has fluidity tends to concentrate at the lower region, a photoresist film having a thickness, for example, of 8 to 10 xcexcm or more is formed at the lower region of the apex portion.
As described above, a pattern having a width of about 1.0 xcexcm must be formed from a photoresist film in order to form a narrow track. It is therefore necessary to form a fine pattern having a width of about 1.0 xcexcm from a photoresist film having a thickness of 8 to 10 xcexcm or more, which has been quite difficult.
In addition, light for exposure at the photolithography is reflected by the electrode film made of permalloy, and the photoresist is sensitive also to this reflected light, which causes breakage of the photoresist pattern and the like. As a result, the top magnetic pole layer can not be formed into the desired configuration. For example, the side walls of the top magnetic pole layer will be in a roundish configuration. According to the related art, it is quite difficult as described above to form a top magnetic pole layer for providing a narrow track structure accurately by controlling the magnetic pole width accurately.
When the top magnetic pole layer is formed using the frame plating process, a problem arises in that the top magnetic pole layer may be difficult to form accurately and may become ununiform in its composition in narrow regions such as regions in the vicinity of boundaries between the side walls of the photoresist pattern and the electrode film.
Japanese Patent Laid-Open Publication No. 9-180127 discloses a technique wherein a reflection preventing film is formed before photoresist to serve as a core mask is applied and wherein the photoresist is applied on the reflection preventing film to make it possible to form a core mask with high dimensional accuracy that is free from the influence of reflected light.
However, this technique is still unable to solve the problem in that the top magnetic pole layer may be difficult to form accurately and may become ununiform in its composition in narrow regions.
Further, according to the above-described technique, it is necessary to remove the reflection preventing film in the region where the top magnetic pole layer is to be formed after the photoresist pattern is formed and before the top magnetic pole layer is formed using a plating process. This increases the number of steps for manufacturing a thin film magnetic head, and the reflection preventing film may be partially left instead of being accurately removed to make it impossible to form the top magnetic pole layer accurately in narrow regions.
A description will now be made on the second problem (the problem of accurate control of the throat height TH). In the method for manufacturing a thin film magnetic head according to the related art, a heating process at a temperature of about 250xc2x0 C. is performed to form the coils 110 and 112. At this heating step, the photoresist layers 109, 111 and 113 melt to cause positional fluctuation of the edges of the photoresist layers 109, 111 and 113 (pattern shift) and deterioration of the profiles of them. Especially, the positional fluctuation is significant because the photoresist layers 109, 111 and 113 are formed with a great thickness.
There is a need for smaller throat heights in order to improve the performance of recording heads and, especially, throat heights of 1.0 xcexcm or less are required for composite thin film magnetic heads for high frequencies in the future. However, in the case of a thin film magnetic head according to the related art, since the throat height is determined by the edge of the photoresist layer 109 at the side of the magnetic pole portion, any positional fluctuation of the edge of the photoresist layer 109 results in the problem of inability to control the throat height accurately as described above.
Further, any positional fluctuation of the edges of the photoresist layers 109, 111 and 113 results in a problem in that the MR height can not be accurately controlled, for example, when the MR height is controlled relative to the position of the edge of the photoresist layer 109 as a reference during the processing of the air bearing surface.
The MR height can be accurately controlled by processing the air bearing surface while monitoring the resistance of the MR film 105. While the throat height can be controlled by converting the resistance of the MR film 105 into the throat height, in order to control the throat height accurately, no error should occur in alignment between the MR film 105 and photoresist layer 109. When there is positional fluctuation of the edges of the photoresist layers 109, 111 and 113 as described above, it is not possible to control the throat height accurately by converting the resistance of the MR film 105 into the throat height.
Further, when there is positional fluctuation of the edges of the photoresist layers 109, 111 and 113 and there is deterioration of the profiles thereof, a problem arises in that the apex angle can not be accurately controlled because the apex angle fluctuates.
In the method for manufacturing a thin film magnetic head according to the related art, the photoresist layer 109 that determines the throat height is etched when the seed layer is etched during the formation of the coils 110 and 112 using a plating process and when the recording gap layer 108 and bottom magnetic pole layer 107 are etched to form the trim structure. This results in a phenomenon that the position of the edge of the photoresist layer 109 at the side of the magnetic pole portion moves back a distance of about 1 to 2 xcexcm, which also leads to the problem in that the accurate control of the throat height becomes difficult.
It is a first object of the invention to provide a method for forming a magnetic pole layer of a thin film magnetic head in which the width of a magnetic pole can be accurately controlled, a thin film magnetic head and a method for manufacturing the same.
It is a second object of the invention to provide a thin film magnetic head in which accurate control of a throat height can be achieved in addition to the first object and to provide a method for manufacturing the same.
A method for forming a magnetic pole layer of a thin film magnetic head according to the invention is a method for forming either of two magnetic pole layers, i.e., first and second magnetic pole layers of a thin film magnetic head comprising first and second magnetic pole layers which are magnetically coupled to each other, which include magnetic pole portions being opposite to each other and being placed in regions of the magnetic pole layers on the side of surfaces thereof facing a recording medium and which are each constituted by at least one layer, a gap layer provided between the magnetic pole portion of the first magnetic pole layer and the magnetic pole portion of the second magnetic pole layer and a thin film coil provided such that at least a part thereof is interposed between the first and second magnetic pole layers in a state of insulation from the first and second magnetic pole layers, the method including the steps of:
forming an electrode film used for forming the magnetic pole layer;
forming a reflection preventing film which is conductive and which has a function of preventing reflection of light for exposure at photolithography on the electrode film;
forming a photoresist pattern for forming the magnetic pole layer on the reflection preventing film using photolithography; and
forming the magnetic pole layer using the photoresist pattern as a mask.
According to the method for forming a magnetic pole layer of a thin film magnetic head of the invention, the reflection of light for exposure at photolithography is prevented by a reflection preventing film. Further, according to the invention, since the reflection preventing film is conductive, the reflection preventing film functions as at least a part of an electrode for forming one of magnetic pole layers, which makes it possible to form the magnetic pole layer accurately even in narrow regions.
A first method for manufacturing a thin film magnetic head according to the invention is a method for manufacturing a thin film magnetic head comprising first and second magnetic pole layers which are magnetically coupled to each other, which include magnetic pole portions being opposite to each other and being placed in regions of the magnetic pole layers on the side surfaces thereof facing a recording medium and which are each constituted by at least one layer, a gap layer provided between the magnetic pole portion of the first magnetic pole layer and the magnetic pole portion of the second magnetic pole layer and a thin film coil provided such that at least a part thereof is interposed between the first and second magnetic pole layers in a state of insulation from the first and second magnetic pole layers, the method including the steps of:
forming the first magnetic pole layer;
forming the gap layer on the first magnetic pole layer;
forming the thin film coil on the first magnetic pole layer in an insulated state; and
forming the second magnetic pole layer on the thin film coil in an insulated state,
the step of forming the second magnetic pole layer including the steps of:
forming an electrode film used for forming the second magnetic pole layer;
forming a reflection preventing film which is conductive and which has a function of preventing reflection of light for exposure at photolithography on the electrode film;
forming a photoresist pattern for forming the second magnetic pole layer on the reflection preventing film using photolithography; and
forming the second magnetic pole layer using the photoresist pattern as a mask.
According to the first method for manufacturing a thin film magnetic head of the invention, the reflection of light for exposure at photolithography is prevented by a reflection preventing film. Further, according to the invention, since the reflection preventing film is conductive, the reflection preventing film functions as at least a part of an electrode for forming a second magnetic pole layer, which makes it possible to form the magnetic pole layer accurately even in narrow regions.
The method for forming a magnetic pole layer of a thin film magnetic head or the first method for manufacturing a thin film magnetic head according to the invention may include the step of removing the reflection preventing film using the photoresist pattern as a mask. In this case, for example, reactive ion etching is used at the step of removing the reflection preventing film.
In the method for forming a magnetic pole layer of a thin film magnetic head or the first method for manufacturing a thin film magnetic head according to the invention, the reflection preventing film may be made of a non-magnetic material, e.g., a non-magnetic nitride such as titanium nitride.
In the method for forming a magnetic pole layer of a thin film magnetic head or the first method for manufacturing a thin film magnetic head according to the invention, one of the magnetic pole layers or the second magnetic pole layer may be formed on the reflection preventing film at the step of forming one of the magnetic pole layers or the second magnetic pole layer. Further, according to the method for forming a magnetic pole layer of a thin film magnetic head of the invention, the reflection preventing film may be made of a magnetic material.
The first method for manufacturing a thin film magnetic head according to the invention may further include the step of forming an insulation layer made of an inorganic insulating material for defining a throat height on the first magnetic pole layer, and the thin film coil may be formed on the insulation layer.
The first method for manufacturing a thin film magnetic head according to the invention may further include the step of forming a magnetoresistive element for reading.
A first thin film magnetic head according to the invention comprises:
first and second magnetic pole layers which are magnetically coupled to each other, which include magnetic pole portions being opposite to each other and being placed in regions of the magnetic pole layers on the side of surfaces thereof facing a recording medium and which are each constituted by at least one layer;
a gap layer provided between the magnetic pole portion of the first magnetic pole layer and the magnetic pole portion of the second magnetic pole layer;
a thin film coil provided such that at least a part thereof is interposed between the first and second magnetic pole layers in a state of insulation from the first and second magnetic pole layers; and
a reflection preventing film which is provided between the gap layer and the second magnetic pole layer, which is conductive and which has a function of preventing the reflection of light for exposure at photolithography.
During the manufacture of the first thin film magnetic head according to the invention, the reflection preventing film prevents the reflection of light for exposure at photolithography. Further, according to the invention, since the reflection preventing film is conductive, the reflection preventing film functions as at least a part of an electrode for forming the second magnetic pole layer, which makes it possible to form the magnetic pole layer accurately even in narrow regions.
The reflection preventing film of the first thin film magnetic head according to the invention may be made of a magnetic material.
The thickness of the reflection preventing film of the first thin film magnetic head according to the invention is, for example, in the range from 20 to 200 xcexcm.
The first thin film magnetic head according to the invention may further include an insulation layer provided between the first magnetic pole layer and the thin film coil and made of an inorganic insulating material for defining a throat height.
The first thin film magnetic head according to the invention may further include a magnetoresistive element for reading.
A second thin film magnetic head according to the invention comprises:
first and second magnetic pole layers which are magnetically coupled to each other, which include magnetic pole portions being opposite to each other and being placed in regions of the magnetic pole layers on the side of surfaces thereof facing a recording medium and which are each constituted by at least one layer;
a gap layer provided between the magnetic pole portion of the first magnetic pole layer and the magnetic pole portion of the second magnetic pole layer; and
a thin film coil provided such that at least a part thereof is interposed between the first and second magnetic pole layers in a state of insulation from the first and second magnetic pole layers,
the gap layer comprising a layer which is non-magnetic and conductive and which has a reflection preventing function for preventing the reflection of light for exposure at photolithography.
A method for manufacturing a second thin film magnetic head according to the invention is a method for manufacturing a thin film magnetic head comprising first and second magnetic pole layers which are magnetically coupled to each other, which include magnetic pole portions being opposite to each other and being placed in regions of the magnetic pole layers on the side of surfaces thereof facing a recording medium and which are each constituted by at least one layer, a gap layer provided between the magnetic pole portion of the first magnetic pole layer and the magnetic pole portion of the second magnetic pole layer and a thin film coil provided such that at least a part thereof is interposed between the first and second magnetic pole layers in a state of insulation from the first and second magnetic pole layers, the method including the steps of:
forming the first magnetic pole layer;
forming the gap layer comprising a layer which is non-magnetic and conductive and which has a reflection preventing function for preventing the reflection of light for exposure at photolithography on the first magnetic pole layer;
forming the thin film coil on the first magnetic pole layer in an insulated state; and
forming the second magnetic pole layer on the thin film coil in an insulated state,
the step of forming the second magnetic pole layer including the steps of:
forming a photoresist pattern for forming the second magnetic pole layer on the gap layer using photolithography; and
forming the second magnetic pole layer using the photoresist pattern as a mask.
In the second thin film magnetic head or the method for manufacturing the same according to the invention, when the second magnetic pole layer is formed on the gap layer including a layer having a reflection preventing function, the gap layer prevents the reflection of light for exposure at photolithography.
In the second thin film magnetic head or the method for manufacturing the same according to the invention, the layer having a reflection preventing function may be made of a non-magnetic nitride such as titanium nitride.
In the second thin film magnetic head or the method for manufacturing the same according to the invention, the gap layer may include the layer having a reflection preventing function and a non-magnetic insulation layer. In this case, the insulation layer is made of, for example, alumina or aluminum nitride.
In the second thin film magnetic head or the method for manufacturing the same according to the invention, the thickness of the layer having a reflection preventing function is, for example, in the range from 20 to 200 xcexcm.
The second thin film magnetic head or the method for manufacturing the same according to the invention may further include an insulation layer provided between the first magnetic pole layer and the thin film coil and made of an inorganic insulating material for defining a throat height.
The second thin film magnetic head or the method for manufacturing the same according to the invention may further include a magnetoresistive element for reading.
Other objects, features and advantages of the invention will become clear enough from the following description.